It is known that organic semiconductors are materials into which charge can be reversibly introduced by the application of electromagnetic energy or chemical dopants. The electronic conductivity of these materials lies between that of metals and insulators, spanning a broad range of 10−9 to 103 Ω−1cm−1. As in traditional inorganic semiconductors, organic materials can function either as p-type or n-type. In p-type semiconductors the majority carriers are holes, while in n-type the majority carriers are electrons.
The vast majority of the prior art has focused on the design, synthesis, and structure-property relationships of p-type organic semiconductor materials, including: oligoacenes, fused oligothiophenes, anthradithiophenes, carbazoles, oligophenylenes, and oligofluorenes, some of which have resulted in field-effect transistors with performance superior to amorphous silicon. In contrast, the development of n-type oligomer and polymer semiconductors has lagged behind p-type materials. In fact, compared to the p-type semiconductors, n-type semiconductors are still not fully developed, and the performances are not satisfactory.
Organic semiconductors that possess a high electron affinity are however also required, as both p- and n-channel materials are required for efficient logic circuits and organic solar cells. Indeed, n-type organic field-effect transistors are envisioned as key components of organic p-n junctions, bipolar transistors, and complementary integrated circuits leading to flexible, large-area, and low-cost electronic applications.
A variety of organic semiconductors have been considered in the art as n-type organic semiconductor materials.
Aromatic tetracarboxylic anhydride and their diimide derivatives were reported among the first n-channel materials. Among the materials of this class, perylenetetracarboxylic diimides having fluorinated side chains showed mobilities up to 0.72 cm2V−1s−1, which only slightly decreased upon air exposure. Air stability, packing grain size and morphology of the deposited films as well as electrical performance can be altered by varying side-chain length, insertion of oxygenated groups and degree of fluorination. However, most of the perylene building blocks, due to the structural rigidity and moderate solubility, do not allow readily structural changes limiting the volume of materials accessible.
Other classes of n-type organic materials have been described such as cyanovinyl oligomers, fullerenes.
J. Am. Chem. Soc. 2009, 131, 16616-16617 describes ambipolar charge transport properties of diketopyrrolopyrrole-copolymers.
A benzothiadiazole-diketopyrrolopyrrole copolymer described in Mater. 2010, 22, 47, 5409-5413, shows high and balanced hole- and electron mobilities of 0.35 cm2V−1s−1 and 0.40 cm2V−1s−1, respectively. Larger electron mobilities values up to 0.85 cm2V−1s−1 were achieved in air for electron-only transporting n-type polymer, called poly{[N,N9-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)}, (Polyera Activink N2200), in a staggered top gate configuration.
N-type semiconductor materials consisting of oligothiophenes bearing fluorinated side groups have been also described in J. Am. Chem. Soc. 2005, 127, 1348 and Angew. Chem. Int. Ed. 2003, 42, 3900. These oligomers showed mobilities up to 0.43 cm2V−1s−1. However, OFETs based on most of these perfluoroaryl and perfluoroalkylaryl substituted materials were unstable in air or suffered from high threshold voltage. Fluorocarbonyl-functionalized oligomers were also described, which showed improved air stability, but lower electron mobilities with respect to fluorinated oligomers.
Oligomers and polymers containing a bithiophene-imide units as inner core have also been described.
For example, J. Am. Chem. Soc. 2008, 130, 9679-9694 describes N-alkyl-2,2′-bithiophene-3,3′-dicarboximide-based homopolymers and copolymers showing p-type or n-type semiconductor behavior depending on the polymeric structure. However, no air-stable devices could be achieved with such materials. In addition, the poor reactivity of the starting dihalogenated bithiophene-imide compounds limits the accessibility of this class of materials.
J. Am. Chem. Soc. 1998, 120, 5355-5362, Tetrahedron Letters 44 (2003) 1563-1565 disclose copolymers containing electron poor 3,4-imido-thienyl blocks alternated to electron rich amino substituted thienyl blocks. No investigation was performed regarding the electrical properties of such copolymers.
N-alkylated poly(dioxopirrolothiophene)s are described in Organic Letters 2004, 6, 19, 3381-3384. However, no proof of an efficient n-type behavior in OFET devices is reported.
Each of the afore mentioned class of materials has poor electrical performances.
WO2008/127029 relates to dioxypirrolo-heterocyclic compounds having the pyrrole moiety fused to the 3,4 position of the thienyl ring and organic electronic devices using said dioxypirrolo-heterocyclic compounds.
Wei Hong et al, “Linear fused dithieno[2,3-b:3′2′-d]thiophene diimides” Organic Letters, vol 13, no. 6, 18 Mar. 2011, pages 1420-1413, discloses a class of linear fully fused dithieno thiophene diimides.
The documents: DE1954550; Ronova Iga A et al: “The effect of conformational rigidity on the initial decomposition temperature of some heterocyclic polyimides”, High Performance Polymers, Institute of Physics Publishing, Bristol GB, vol. 14, No. 2, 1 Jan. 2002, pages 195-208; and Gaina C. et al, “Polyimides containing 1,4-dithiine units and their corresponding thiophene 2,3,4,5 tetracarboxylimide units” High Performance Polymers, Institute of physics publishing, Bristol GB, vol. 11, No. 2, 1 Jun. 1999, pages 185-195, disclose polymeric diimmide compounds in which the member connecting the polymer repeating units is the N-imidic substituent. The three last cited documents do not mention any semiconductor property of the compounds therein disclosed.
WO2006/094292 discloses thienopyridine compounds capable of modulating the stability and/or activity of hypoxia inducible factor, pharmaceutical compositions comprising said compounds and chemical intermediates useful for preparing said compounds. Among said chemical intermediates, specific compounds having a 4,6-dioxo-thieno[2,3-c]pyrrole nucleus are disclosed.
EP0467206 discloses specific compounds having a 4,6-dioxo-thieno[2,3-c]pyrrole nucleus and their use as herbicide.
However, WO2006/094292 and EP0467206 do not teach the semiconductor properties of said compounds.
Therefore, there is still the need of n-type organic semiconductor materials or compounds that possess higher electron mobility properties.